The invention relates to a fuel injection pump having a cylinder and a cylindrical pump piston reciprocating within the cylinder, which piston on its outer cylindrical surface includes at least one longitudinal groove extending from one end surface of the piston and at least one oblique groove oriented obliquely relative to the end surface and extending over a portion of the circumference defined by the outer cylindrical surface. The cylinder has at least one opening which can be made congruent with one of the grooves. The congruence is controlled by rotation of the piston, which in turn is effected by a rotational device controlled by an electrical control unit.
In fuel injection pumps of this kind, an orientation of the opening in the cylinder wall is produced with the longitudinal groove and the obliquely oriented groove because of the rotatability of the pump piston between defined stops. The rotatability is effected with the aid of the governor rod, such that in one terminal position of the piston the opening is brought into congruence with the longitudinal groove, and in the other terminal position it is brought into congruence with the pump piston part, which, in a known manner, determines the starting fuel injection quantity of the pumping element. The pump piston part makes this determination, for example, by means of said oblique groove, or by means of an additional starting groove, or by means of omitting said oblique groove on the piston part being in congruence with the opening in the cylinder wall.
In electronically regulated fuel-injection pumps, however, interruption of the satisfactory functioning of the circuit or of the control device increasingly occurs. In these cases, there is the possibility that the pump pistons may be brought into their position of maximum rotation, which is incorrect for the conditions in the internal combustion engine. This can cause an excessive supply of fuel, thus resulting in overspeeding and the destruction of the engine associated with this pump.